So I was looking at a pump action reaper guide and realized there wasn't any one that was exact for the champion!
Here's the pic of my finished one. Spray paint job is crappy because me and my dad didn't have the stuff to take it apart. Sorry.
https://cdn.discordapp.com/attachments/352852966945849355/363811710718443520/0930171713a.jpg
As you can probably see. All I did was add a pipe barrel. You'll want about a 7 inch or so barrel of 1 inch inner diameter PVC. At the end cut out a 1 inch wide and long channel so the dart tooth can go through. Slide that in the barrel, make sure it fires with it in, then screw it on in. next up is the pumpy grip. Take a 1 1/4th inch length of pvc 3 inches long and slide it over. Prime back your gun and get a small rectangular length of just about anything. The gun I made used aluminium strips. They're normally about 13-12 inches long but if it's too long you can always cut it down. Screw the strip into the priming handle on the top but not too far or it'll prevent it from priming. Now screw the other end into the 1 1/4th inch pvc so when you pull that pvc back it primes the gun. Repeat on the other end and congrats, you have a home made pump action nerf gun. It's fairly simple but I didn't see any posts of people doing it on here so far so I figured I'd make one here. Any other modifications to it you need to do beforehand.
EDIT: I forgot something! You need to cut off the tip of the barrel. the first little inch that's smaller then the rest. You also need to dremme/drill out a bit of that orange front piece that the pump slides into. It'll prevent it from going all the way back. You'll know what I mean once I make one. Just use a drill or something and you'll be fine